Find the sum S9 of the first 9 terms of the geometric sequence 4, −2, 1, …
Sequences & series worksheet with answers
1.Easy
a₁ = 4r = −0.5n = 9
S9 =
2.Easy
Find the sum S of the infinite series Σk=1∞ 12·(−2/5)ᵏ.
a = 12r = −2/5k₀ = 1
S =
3.Medium
Apply the ratio test to Σk=1∞ 3ᵏ·k!/kᵏ. Find L = lim |ak+1/ak|.
ak = 3ᵏ·k!/kᵏ
L =
4.Medium
Apply the ratio test to Σk=1∞ k·2ᵏ/3ᵏ. Find L = lim |ak+1/ak|.
ak = k·2ᵏ/3ᵏ
L =
5.Hard
f(x) = sin x is approximated at x = 1 by its Maclaurin polynomial of degree n. With the Lagrange bound M·|x|ⁿ⁺¹/(n + 1)! and M = 1, find the smallest degree n that guarantees an error below 1 × 10⁻⁶.
f(x) = sin xx = 1M = 1ε = 1 × 10⁻⁶
n =
6.Hard
Recognise the series and find its sum: S = Σk=1∞ k·0.25ᵏ.
ak = k·0.25ᵏ
S =
Answer key
- 1. S9 = 2.672
- 2. S = −3.429
- 3. L = 1.104
- 4. L = 0.6667
- 5. n = 9
- 6. S = 0.4444
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